MEG recordings of DC fields using the signal space separation method (SSS).

Stationary SQUID sensors record time-varying magnetic fields only. Any DC sources, such as magnetic impurities on the scalp or physiological DC currents, are invisible in conventional MEG with stationary sources and sensors. However, movement of the subject relative to the measurement device transforms the DC fields into time-varying MEG signals, which are either signals of interest from biomagnetic sources, or movement artifacts when caused by magnetic residue on the head.

Suppression of interference and artifacts by the Signal Space Separation Method.

Multichannel measurement with hundreds of channels oversamples a curl-free vector field, like the magnetic field in a volume free of sources. This is based on the constraint caused by the Laplace's equation for the magnetic scalar potential; outside of the source volume the signals are spatially band limited. A functional solution of Laplace's equation enables one to separate the signals arising from the sphere enclosing the interesting sources, e.

Neuromagnetic somatosensory responses to natural moving tactile stimulation.

Objective: To explore the somatosensory cortical responses to natural moving tactile stimulation in adult subjects using magnetoencephalography.

Methods: We measured cortical somatosensory magnetic evoked fields (SEFs) to moving tactile stimuli by a brush over the right thumb once every 1.5 s in seven subjects.

Cortical control of human motoneuron firing during isometric contraction.

We recorded whole scalp magnetoencephalographic (MEG) signals simultaneously with the surface electromyogram from upper and lower limb muscles of six healthy right-handed adults during voluntary isometric contraction. The 15- to 33-Hz MEG signals, originating from the anterior bank of the central sulcus, i.e.

Movement-related slow cortical magnetic fields and changes of spontaneous MEG- and EEG-brain rhythms.

Cortical activity was recorded from 5 healthy adults with a 122-channel whole-head magnetometer while the subjects performed during unilateral finger movements at self-paced intervals exceeding 6 s. The readiness field (RF) started over the contralateral somatomotor area 0.3-1 s prior to the movement onset in subjects (Ss) 1, 2, and 4, and culminated in the motor field (MF) 30 ms after it (Ss 1-4).